@vertex
fn main(@builtin(vertex_index) VertexIndex: u32) -> @builtin(position) vec4<f32> {
    const pos = array<vec2f, 3>(
        vec2(0.0, 0.5),
        vec2(-0.5, -0.5),
        vec2(0.5, -0.5) 
    );
    return vec4<f32>(pos[VertexIndex], 0.0, 1.0);
}